Remove 'static bound on contract ensures closure

The `'static` bound on the closure of `build_check_ensures` prevented
some patterns of contracts from type checking, without a clear
reason for doing so. As such, this change removes the `'static` bound.

Author: dawidl022

library/core/src/contracts.rs

@@ -18,7 +18,7 @@ pub use crate::macros::builtin::{contracts_ensures as ensures, contracts_require
 #[lang = "contract_build_check_ensures"]
 pub const fn build_check_ensures<Ret, C>(cond: C) -> C
 where
-    C: Fn(&Ret) -> bool + Copy + 'static,
+    C: Fn(&Ret) -> bool + Copy,
 {
     cond
 }

tests/ui/contracts/ensures-lifetime.rs

@@ -0,0 +1,30 @@
+//@ run-pass
+//@ compile-flags: -Zcontract-checks=yes
+
+#![feature(core_intrinsics)]
+#![feature(contracts)]
+//~^ WARN the feature `contracts` is incomplete and may not be safe to use
+//and/or cause compiler crashes [incomplete_features]
+#![allow(unused)]
+
+// Regression test to allow contract `ensures` clauses to reference non-static
+// references and non-static types. Previously, contracts in the below functions
+// would raise type/lifetime errors due a `'static` bound on the `ensures`
+// closure.
+
+extern crate core;
+use core::contracts::ensures;
+
+#[ensures(|_| { x; true })]
+pub fn noop<T>(x: &T) {}
+
+#[ensures(move |_| { x; true })]
+pub fn noop_mv<T>(x: &T) {}
+
+#[ensures(|_| { x; true })]
+pub fn noop_ptr<T>(x: *const T) {}
+
+#[ensures(move |_| { x; true })]
+pub fn noop_ptr_mv<T>(x: *const T) {}
+
+fn main() {}

tests/ui/contracts/ensures-lifetime.stderr

@@ -0,0 +1,11 @@
+warning: the feature `contracts` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/ensures-lifetime.rs:5:12
+   |
+LL | #![feature(contracts)]
+   |            ^^^^^^^^^
+   |
+   = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+